Generates pseudo-random numbers.
Standard C Library (libc.a)
#include <stdlib.h>
int rand
void srand ( Seed)
unsigned int Seed;
The rand subroutine generates a pseudo-random number using a multiplicative congruential algorithm. The random-number generator has a period of 2**32, and it returns successive pseudo-random numbers in the range from 0 through (2**15) -1.
The srand subroutine resets the random-number generator to a new starting point. It uses the Seed parameter as a seed for a new sequence of pseudo-random numbers to be returned by subsequent calls to the rand subroutine. If you then call the srand subroutine with the same seed value, the rand subroutine repeats the sequence of pseudo-random numbers. When you call the rand subroutine before making any calls to the srand subroutine, it generates the same sequence of numbers that it would if you first called the srand subroutine with a seed value of 1.
Seed | Specifies an initial seed value. |
Upon successful completion, the rand subroutine returns the next random number in sequence. The srand subroutine returns no value.
There are better random number generators, as noted above; however, the rand and srand subroutines are the interfaces defined for the ANSI C library.
The following functions define the semantics of the rand and srand subroutines, and are included here to facilitate porting applications from different implementations:
static unsigned int next = 1; int rand( ) { next = next * 1103515245 + 12345; return ((next >>16) & 32767); }
void srand (Seed) unsigned int Seed; { next = Seed; }
The drand48, erand48, lrand48, nrand48, mrand48, jrand48, srand48, seed48, or lcong48 subroutine, random, srandom, initstate, or setstate (random, srandom, initstate, or setstate Subroutine) subroutine.
Subroutines Overview in AIX 5L Version 5.2 General Programming Concepts: Writing and Debugging Programs.